motor 3p running two run caps 15mf to single phase not running

[marc8]

hi help required if poss?

called out machine not running food shredder quite small

found 15mf cap lid was cracked (cap no capacitance on terminals)

2 caps in series 15mf motor taken of one cap

so bridged out thermal overload got machine to run very slow stopped.

could not get 15mf cap but other cap ok

managed to get 30mf cap so took out bad cap put in 30mf cap instead of using 2 caps

used 15mf cap still for the motor as was before.

set up was

1wire going to first cap through cap at this point 1 cable went 9 terminal board (motor winding W)

then from first cap to second cap & other wire out to terminal board not motor.

as explained replaced with 30mf now not in series as to make 30mf as before but running 15mf for motor

motor ran for whole two days no probs at all going back to look again could be other cap was on way out
but not sure any help would be great??

also do have 3 phase available on site could remove this & put in DOL starter & do away with single phase.

your thoughts would be most welcome

 

[LeeH]

hi help required if poss?

called out machine not running food shredder quite small

found 15mf cap lid was cracked (cap no capacitance on terminals)

2 caps in series 15mf motor taken of one cap

so bridged out thermal overload got machine to run very slow stopped.

could not get 15mf cap but other cap ok

managed to get 30mf cap so took out bad cap put in 30mf cap instead of using 2 caps

used 15mf cap still for the motor as was before.

set up was

1wire going to first cap through cap at this point 1 cable went 9 terminal board (motor winding W)

then from first cap to second cap & other wire out to terminal board not motor.

as explained replaced with 30mf now not in series as to make 30mf as before but running 15mf for motor

motor ran for whole two days no probs at all going back to look again could be other cap was on way out
but not sure any help would be great??

also do have 3 phase available on site could remove this & put in DOL starter & do away with single phase.

your thoughts would be most welcome

Yes you can bin the caps an go DOL. Just make sure you check the motor plate so you have the star/delta links in correctly.

Also note if the machine is 1PH you will need to mod the isolator and switchgear. Contractor, overload etc.

 

[Marvo]

I'm confused on at least two accounts, firstly 3-phase motors generally don't have supply capacitors, they get rotation from the angle of the phases not via a capacitor. Secondly 2 x 15uF caps in series don't equate to a single 30uF cap.

Capacitors in series 1/Ctotal = 1/C1 + 1/C2

Capacitors in parallel Ctotal = C1 + C2

 

[Lucien Nunes]

A schematic is worth a thousand words. I cannot follow your description reliably but it sounds as though what you have wired up is not the same as the original at all. Two 15µF caps in series makes 7.5µF at twice the rated voltage, but if there is a connection to the motor from the point at which the two caps join then they're not 'in series' either and must only be replaced with two 15µFs. If you use the wrong caps the motor might run but will lack power and may burn out due to wrong winding currents.
15µF motor-run caps are easy to get and about £5-10 each. E.g. Buy Polypropylene Film Capacitors MRA440 motor run/start cap,15uF 440Vac RS MRA/440/15UF/C online from RS for next day delivery. and many like it. Make sure the voltage rating of the new cap is no less than the original. Note that the voltage across the capacitor when running can be higher than the mains voltage.

 

[Knobhead]

I can't make head nore tail of the OP

 

[Lucien Nunes]

I think he has a small 3-phase or at least split-phase motor with one start cap and one run cap, or something similar, running on single phase supply. When one cap visibly failed he replaced it with a cap of twice the value, connected differently, and now it doesn't work...

 

[telectrix]

should have used the correct components. when i need a hip replacement i want a human one, not a dog one, or else i'll be running round shagging peoples' legs.